#!/usr/bin/python

nm=raw_input("please enter the width of the cube, in  nanometers: ")
mass=raw_input("Please enter the mass of one mole of the molecule, in g/mol: ")
nmol=raw_input("Please enter the number of molecules: ")

nm=float(nm)
mass=float(mass)
nmol=float(nmol)

density=(mass*nmol/(6.022e23))/((nm*1.0e-7)**3)

print "%.3f g/cm^3" % density